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Swim with Turtles, the most popular visitor to The Great Barrier Reef, in Port Douglas

The Great Barrier Reef is home to six of the world’s seven turtle species; the loggerhead, green, hawksbill, olive ridley, leatherback and the endemic flatback, which is only found in waters off Northern Australia.

Turtles have been in our ocean since the time of the dinosaurs, over 150 million years ago. They can live up to 100 years old and are air-breathing reptiles, meaning they must come to the surface every few hours to breathe. They also come ashore to lay eggs.

When female turtles are ready to lay nests, they return to the same beach from which they were born up to 30 years earlier. They crawl ashore to dig an egg chamber 30-60 centimetres vertically deep into the sand to lay the clutch of eggs, which can comprise up to 120 eggs. As this is the only maternal care she provides her offspring, she spends a lot of time digging the perfect nest and burying the eggs, sometimes taking all night. The exhausted female then returns to the ocean.

During incubation, lasting up to 12 weeks, the temperature of the sand determines the sex of the hatchlings. A nest of 29.5 degrees will produce an even split of males and females, slightly cooler temperatures produces males, and nests hotter than 30 degrees will produce all females. On a full moon the hatchlings begin to emerge. Using the light of the moon upon the ocean’s horizon, the little hatchlings begin their dash for the sea. During this short run, the hatchlings are besieged by birds, dogs, crabs and other predators out for an easy meal. Upon reaching the sea the hatchlings embark on a swimming frenzy for the outer sea where they hide under seaweed and other flotsam, drifting on currents for the next 10 years or more. Once their shell is 20-40 centimetres in length they return to inshore reefs to feed. They remain in these areas until they reach sexual maturity and the cycle begins again.

All turtle species within Australia are classified as endangered or vulnerable by the AustralianEnvironment Protection and Biodiversity Conservation Act 1999. Scientists estimate that only 1 in 1000 hatchlings will survive to reach sexual maturity due to natural and human threats. Human influenced threats include; climate change, marine debris, poaching of nests and boat strikes.

There are two breeding stocks of green turtles within the Great Barrier Reef, a northern stock and a southern stock. The northern subpopulation breed on Raine Island and Moulter Cay, while the southern subpopulation nest in the Capricorn/Bunker group of islands. Loggerhead turtles also nest in the Southern Great Barrier Reef Marine Park near the Capricorn/Bunker group of islands and off Bundaberg.

Other facts:

The largest of turtle species, the leatherback, has been compared to the size of a VW beetle (a small car). Its shell, or carapace, has measured up to 2.5 metres. Unlike the other turtle species whose carapace is made from bones called scutes, the leatherback’s carapace is leather, hence its name.

The green turtle is named for the colour of its fat, which it is thought to obtain from all the algae they eat.